1. Field of the Invention
This invention relates to a cam to be shrunk on a camshaft and to a process for sintering such cam.
2. Description of the Prior Art
A practice in which cams of a camshaft are made as separate components and shrunk on a preferably tubular shaft will afford considerable advantages as regards the manufacture and the weight of the camshaft. For such a manufacture of the camshaft the cams must be made in a relatively simple manner and with the required precision from a material which will withstand the loads to be encountered. Cams made as separate parts may be made by a sintering process. But it is difficult to provide sintered cams which have the required strength and the required precision. To provide a material having the required strength, the porosity of the sintered member must be low and the alloying elements added to the steel must be distributed as homogeneously as possible. Said requirements can be met by a liquid-phase sintering process because the sintering in the liquid phase ensures a high diffusion rate and a quick coagulation at the pores. But the resulting high-density sintering involves a substantial shrinkage so that the sintered members may not have the required dimensional stability. For this reason, shrink-on cams cannot be made by a liquid-phase sintering process in which a liquid phase is permanently maintained. Besides, known high-strength sintered steels, which contain, e.g., 4.5 weight percent nickel, 1.5 weight percent copper, 0.5 weight percent molybdenum and 0.4 to 0.7 weight percent carbon, do not meet the strength requirements for cams and exhibit bad tempering properties. Tests have shown that cams made of such sintered steels when subjected to the load reversals to be expected have a useful life of less than 150 hours, which is entirely unsatisfactory.